The compound 1-chloro-4-(β-D-glucopyranos-1-yl)-2-[4-((S)-tetrahydrofuran-3-yloxy)-benzyl]-benzene (in the following referred to it as “compound A”) is described in the international patent application WO 2005/092877 and has the chemical structure according to formula A

The compounds described therein have a valuable inhibitory effect on the sodium-dependent glucose cotransporter SGLT, particularly SGLT2.
The international patent application WO 2006/120208 describes various methods of synthesis of SGLT2 inhibitors, inter alia of the compound A.
A crystalline form of the compound A and a method for its preparation are described in the international application WO 2006/117359. As preferred solvents for example methanol, ethanol, isopropanol, ethyl acetate, diethylether, acetone, water and mixtures thereof are described for the crystallization process.
In the synthesis of the compound A, for example according to WO 2006/120208, it is observed that certain impurities may be found in the final substance. Furthermore it is found that crystallization processes as described in the WO 2006/117359 decrease the content of impurities and increase the purity of the compound, but not in a totally satisfactory manner.
It is well known to the one skilled in the art that in the pharmaceutical field highly pure compounds are desired. A very high purity may improve the stability in long-term storage. On the other hand impurities may be attributed to unwanted physico-chemical properties, for example hygroscopicity, or pharmacological side effects.